Vit-c as the cofactor of TET enzymes treatment can maintain demethylation of CNS2, and stabilize the expression of Foxp3 in CD8+ Tregs, thus promoting expression of CD25, Nrp1, Helios, CTLA-4 and PD-1 in vitro, preventing GVHD and maintaining the GVL effects (23). The gene discussed is CTLA4; the disease is graft versus host disease.